Method and device for measuring the permeability of a drying wire to air

Abstract

A method and device for measuring the permeability of a drying wire to air in which the measurement is carried out continuously while the drying wire moves. The drying wire is guided to run so that it passes over a blow box and a measurement box free of contact, and the pressure in the measurement box and/or the relative change in the pressure is/are measured when the blow box is creating a pressure differential between the blow box and the measurement box in the vicinity of the wire. The pressure and/or the relative change in the pressure is/are compared with earlier measurement results and/or starting values (reference values). The permeability to air of the drying wire is determined on the basis of comparison of the pressure and/or of the relative change in the pressure, and the contact-free measurement is produced by guiding the flow into or out of the measurement box to pass through a gap between the measurement box and the drying wire.

I claim: 
     
       1. A method for measuring the permeability of a drying wire to air during movement of the drying wire, comprising the steps of: guiding the drying wire to pass over a blow box and a measurement box without the drying wire contacting the blow box or the measurement box, the measurement box being spaced from the drying wire such that air flows from or into the measurement box through a gap between the measurement box and the moving drying wire,   generating a pressure differential between the blow box and the measurement box such that the pressure in the measurement box is relative to the permeability of the drying wire,   measuring at least one of the pressure in the measurement box and a relative change in the pressure in the measurement box,   comparing at least one of the measured pressure in the measurement box and relative change in the pressure in the measurement box to a previously measured or reference pressure values or a previously measured or reference relative pressure change value, and   determining the permeability of the drying wire to air on the basis of the comparison of at least one of the pressure in the measurement box and the relative change in the pressure in the measurement box.   
     
     
       2. The method of claim 1, further comprising the steps of: arranging the blow box and measurement box in a paper machine, and   conducting the measuring step when the paper machine is running at a full running speed.   
     
     
       3. The method of claim 1, further comprising the steps of: arranging the blow box and measurement box in a drying wire manufacturing machine, and   conducting the measuring step when the drying wire manufacturing machine is running at a crawling speed.   
     
     
       4. The method of claim 1, wherein the step of generating the pressure differential between the blow box and the measurement box comprises the step of directing air from the blow box to produce a positive pressure in an area between the drying wire and the blow box, further comprising the step of: arranging the measurement box on an opposite side of the drying wire from the blow box such that the air flow through the drying wire into the measurement box is a function of the permeability of the drying wire.   
     
     
       5. The method of claim 4, further comprising the steps of: guiding the drying wire over a wire guide roll, and   arranging the blow box and the measurement box in an area of an inlet nip of the drying wire and the wire guide roll, the inlet nip being subjected to a positive pressure by the effect of pumping by the drying wire.   
     
     
       6. The method of claim 1, wherein the step of generating the pressure differential between the blow box and the measurement box comprises the step of directing air from the blow box to produce a negative pressure in an area between the drying wire and the blow box, further comprising the step of: arranging the measurement box on an opposite side of the drying wire from the blow box such that the air flow through the drying wire from the measurement box is a function of the permeability of the drying wire.   
     
     
       7. The method of claim 6, further comprising the steps of: guiding the drying wire over a wire guide roll, and   arranging the blow box and the measurement box in an area of an outlet nip of the drying wire and the wire guide roll, the inlet nip being subjected to a negative pressure by the effect of the evacuation of air produced by the drying wire.   
     
     
       8. The method of claim 1, wherein the step of generating the pressure differential between the blow box and the measurement box comprises the step of directing air from the blow box to produce a negative pressure in an area between the drying wire and the blow box, further comprising the step of: arranging the measurement box on the same side of the drying wire as the blow box such that the air flow from the measurement box through the gap between the measurement box and the drying wire is a function of the permeability of the drying wire.   
     
     
       9. The method of claim 1, further comprising the steps: passing the drying wire over a pair of support rolls or glide faces spaced from each other,   arranging the blow box and measurement box between the support rolls or glide faces, and   conducting the measuring step when the drying wire is running at a crawling speed.   
     
     
       10. The method of claim 1, wherein the measuring step comprises the step of measuring the permeability of the drying wire at a plurality of discrete locations in the cross direction of the drying wire. 
     
     
       11. The method of claim 1, wherein the measuring step comprises the step of measuring the permeability of the drying wire substantially across the entire width of the drying wire to obtain a continuous permeability profile in the cross-machine direction. 
     
     
       12. A device for measuring the permeability of a drying wire to air while the drying wire is moving, comprising a blow box arranged in the vicinity of and spaced from the drying wire such that the drying wire passes over said blow box without contacting said blow box,   a measurement box spaced from the drying wire such that a gap is formed between said measurement box and the drying wire and the drying wire passes over said measurement box without contacting said measurement box, said blow box being arranged to generate a pressure differential between said blow box and said measurement box whereby the pressure in said measurement box is relative to the permeability of the drying wire, and   measurement means for measuring at least one of the pressure in said measurement box and a relative change in the pressure in said measurement box, the permeability of the drying wire being determinable from said measured pressure in said measurement box and said measured relative change in the pressure in said measurement box.   
     
     
       13. The device of claim 12, wherein said blow box comprises nozzles arranged at edges of said blow box for producing edge blowings, said edge blowings causing a middle area of said blow box between said edges to be subjected to a positive pressure greater than the pressure in said measurement box. 
     
     
       14. The device of claim 12, wherein said blow box comprises nozzles arranged at edges of said blow box for producing edge blowings, said edge blowings causing a middle area of said blow box between said edges to be subjected to a negative pressure less than the pressure in said measurement box. 
     
     
       15. The device of claim 12, wherein the device is situated in a paper machine, the paper machine including a wire guide roll over which the drying wire runs, said blow box and said measurement box being arranged in an area of an inlet nip defined by said wire guide roll and the drying wire. 
     
     
       16. The device of claim 12, wherein the device is situated in a paper machine, the paper machine including a wire guide roll over which the drying wire runs, said blow box and said measurement box being arranged in an area of an outlet nip defined by said wire guide roll and the drying wire. 
     
     
       17. The device of claim 12, wherein said blow box comprises a plurality of blocks and said measurement box comprises a plurality of blocks, each of said blocks of said measurement box being aligned with a respective one of said blocks of said blow box, said measurement means being arranged to measure the pressure in each of said measurement boxes in order to obtain a permeability profile of the drying wire in the cross direction of the drying wire. 
     
     
       18. The device of claim 12, further comprising frame means for fixing said blow box and said measurement box in respective fixed positions, and   guide means for guiding the drying wire over said blow box and said measurement box, said guide means being selected from the group consisting of a support roll and a glide face.   
     
     
       19. The device of claim 12, wherein said measurement means measure the pressure in said measurement box and a relative change in the pressure in said measurement box. 
     
     
       20. The device of claim 12, wherein said measurement means measure only a relative change in the pressure in said measurement box.